Satellite based navigation systems are widely used. Global navigation satellite systems (GNSS) include Global Positioning System (GPS) (United States), GLONASS (Russia), Galileo (Europe), and COMPASS (China). A GNSS often involves a plurality of satellites orbiting the Earth, and the plurality of satellites form a constellation of satellites. Each satellite transmits a navigation message periodically that can be received and used by a GNSS receiver to derive position, velocity, and/or time. For example, GPS navigation systems can acquire and track GPS satellite signals so that range measurements can be made between several satellites and a GPS receiver in order to compute a location for the receiver. A metric of acquisition performance is time to first fix (TTFF). The TTFF may depend on the accuracy of the receiver's previous estimate of GPS time within the receiver's local timing system.
Electronic devices (e.g., a mobile phone, a tablet computer, a camera, etc.) often include a GPS receiver. Different clocks may be used for different function modules in such electronic devices. For example, a clock used for the GPS receiver corresponds to a local clock of the GPS receiver, while other clocks may correspond to external clocks relative to the GPS receiver. The local clock of the GPS receiver provides a reference frequency source so as to generate a local carrier that is used for GPS signal down conversion in a radio frequency (RF) front end and GPS signal mixing in a baseband.